Hi João

> Any simplification to the implementation that keeps the
> "keep original window intent" behavior across xref
> intermediate buffers is very welcome.

Thanks for the explanation.  Now I understand better the intent in
xref--show-pos-in-buf.  Generally, I'd like to see the “keep original
window intent” behavior in more places, e.g. in *Occur*, *grep*, etc.
Based on your explanation, I've been able to write the patch that does
the following:

1. simplifies ‘xref--show-pos-in-buf’ while at the same time
   preserves the current behavior and respects user's customization
   of display actions;

2. makes the xref buffer non-obtrusive like *Completions*
   in xref--show-xref-buffer;

3. turns the existing arg QUIT of xref-goto-xref into a prefix arg,
   so a natural key sequence ‘C-u RET’ will quit the window.
   This is similar to the prefix arg of quit-window.